Optical Engineering, Research Institute of Molecular Pathology (IMP), Vienna, Austria.
PLoS One. 2009 Dec 1;4(12):e7963. doi: 10.1371/journal.pone.0007963.
It has been shown that thin metal-based films can at certain frequencies act as planar near-field lenses for certain polarization components. A desirable property of such "lenses" is that they can also enhance and focus some large transverse spatial frequency components which contain sub-diffraction limit details. Over the last decade there has been much work in optimizing designs to reduce effects (such as material losses and surface roughness) that are detrimental to image reconstruction. One design that can reduce some of these undesirable effects, and which has received a fair amount of attention recently, is the stacked metal-dielectric superlens. Here we theoretically explore the imaging ability of such a design for the specific purpose of imaging a fluorescent dye (the common bio-marker GFP) in the vicinity of the superlens surface. Our calculations take into consideration the interaction (damping) of an oscillating electric dipole with the metallic layers in the superlens. We also assume a Gaussian frequency distribution spectrum for the dipole. We treat the metallic-alloy and dielectric-alloy layers separately using an appropriate effective medium theory. The transmission properties are evaluated via Transfer matrix (-matrix) calculations that were performed in the MatLab and MathCad environments. Our study shows that it is in principle possible to image fluorescent molecules using a simple bilayer planar superlens. We find that optimal parameters for such a superlens occur when the peak dipole emission-frequency is slightly offset from the Surface Plasmon resonance frequency of the metal-dielectric interfaces. The best resolution is obtained when the fluorescent molecules are not too close (>/ approximately 10 nm) or too far (>/approximately 30 nm) from the superlens surface. The realization and application of a superlens with the specified design is possible using current nanofabrication techniques. When combined with e.g. a sub-wavelength grating structure (such as in the far-field superlens design previously proposed [1]) or a fast near-field scanning probe, it could provide a means for fast fluorescent imaging with sub-diffraction limit resolution.
已经证明，在某些频率下，薄金属基膜可以作为平面近场透镜，对某些偏振分量起作用。这种“透镜”的一个理想特性是，它们还可以增强和聚焦某些含有亚衍射极限细节的大横向空间频率分量。在过去的十年中，人们一直在努力优化设计，以减少对图像重建不利的影响（如材料损耗和表面粗糙度）。一种可以减少这些不良影响的设计是堆叠金属-电介质超透镜，最近受到了相当多的关注。在这里，我们从理论上探讨了这种设计的成像能力，特别是为了在超透镜表面附近对荧光染料（常见的生物标记 GFP）进行成像。我们的计算考虑了振荡电偶极子与超透镜中的金属层的相互作用（阻尼）。我们还假设偶极子的频率分布为高斯分布。我们使用适当的有效介质理论分别处理金属合金和电介质合金层。传输特性通过在 MatLab 和 MathCad 环境中执行的传递矩阵（-矩阵）计算进行评估。我们的研究表明，原则上可以使用简单的双层平面超透镜对荧光分子进行成像。我们发现，对于这种超透镜，当偶极子的峰值发射频率稍微偏离金属-电介质界面的表面等离子体共振频率时，最佳参数就会出现。当荧光分子离超透镜表面不太近（>/约 10nm）或太远（>/约 30nm）时，分辨率最佳。使用当前的纳米制造技术可以实现具有指定设计的超透镜，并将其应用于实际中。当与例如亚波长光栅结构（如以前提出的远场超透镜设计[1]）或快速近场扫描探针结合使用时，它可以提供一种具有亚衍射极限分辨率的快速荧光成像方法。
